Well, I'm not one for advocating that wizards facilitates people showing up to events unprepared.

I think the problem is that if no one sees the set you end up asking really stupid questions because you have no idea what the quality of the cards in general are.

Like if I'm playing RtR I know that 4 toughness is really darn hard to kill and 5 or more is god tier. But what if the format is removal heavy or removal light? What if there are a bunch of cheap aggro creatures making the format really fast and pull some bomby mythic and have no idea if it's viable in the format?

You don't end up asking the right questions and evaluating cards on their own right, instead you're forced to not know what the hell you're meant to play around. You just sort of slam cards and pray they are good. I imagine it would be a shit feeling to go "Oh, you got me, I didn't know they printed giant growth in this set. I guess I'll just have to remember next time."